Switch assembly



Nov. 17, 1942. v. H. HARDY SWITCH ASSEMBLY Filed Oct. 25, 1940 Bnmmtor wag/222 91. fila ldy (Ittomegs 20 FW 4/ 5a 6 Z M/ J |.[1 E E a 11% w 0. \I\ 0 M w J 4 w J 6 Z a Patented Nov. 17, 1942 SWITCH ASSEllIBLY Vaughn H. Hardy, Rochester, N. Y., assignor to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application October 25, 1940, Serial No. 362,815

9 Claims.

The present invention relates generally to switches and more particularly to certain improvements in a thermally actuated timing switch which is primarily intended for use in a control system for a domestic oil burner.

One of the objects of the invention is to provide a switch of this type which is extremely simple in construction and reliable in operation.

A further object is to provide a switch of this type which is compensated for ambient temperature changes and in which there will be a positive opening and closing of contacts with minimum sparking.

A still further object is to provide a further set of switch contacts for a purpose to be set forth hereinafter which are opened and closed by movement of a portion of the thermally actuated switch.

Other objects and features of the invention together with the advantages thereof will be apparent or will be specifically pointed out in the description of the embodiment illustrated in the accompanying drawing in which:

Figure 1 is a perspective view of the switch as sembly.

Figure 2 is an enlarged horizontal sectional view thereof taken substantially on line 2--2 of Figure 1.

Figure 3 is a fragmentary end elevation taken as indicated by line 3-3 in Figure 1.

Referring now to the drawing, the entire switch unit or assembly may be conveniently mounted on an insulating base 2 such as carries other units of the oil burner control which are not a part of the present invention. The thermally actuated switch includes two parallel bimetal members 4 and 6 which are spaced at their lower ends by the angled bracket 8 to which they may be riveted. The bracket 8 is pivoted intermediate the members 4 and 6 on a pin in secured to the base 2.

It will be understood that each of the bimetal members 4 and 6 is constituted in known manner of materials having different coefiicients of expansion and contraction on temperature changes,

and in the present construction such members are so arranged for reasons to be noted hereinafter that the upper ends thereof will both tend to move in the same relative direction when subjected to the same temperature changes.

An electric heater assembly is associated with and mounted closely adjacent one side of the bimetal member 4. This assembly preferably consists of a resistance wire. l2 wound on a mica strip l4 which is placed between the larger mica 55 sheets I6 and ill with such parts clamped together by the metal plate 20 which is folded tightly around the mica sheets l6 and 18. This electric heater assembly may be secured to the bracket 8 by the same rivets 22 which secure the bimetal member 4 thereto.

A contact spring 24 is riveted at its lower end to the opposite side of the bimetal member 4 with a contact 26 secured to the upper free end of such spring and extending through a slot 23 in the upper end of the bimetal member 4. An iron armature 30 is riveted to the upper free end of the bimetal member 4 and is formed with an opening to clear an enlarged portion of the contact 26.

To cooperate with the armature 30, a magnet 32 is secured to the base 2 by means of a bracket 34 which may be riveted to the base 2 with a tongue 36 extending through the base to provide for an electrical connection thereto. The magnet 32 may be of U-form with a rivet or bolt 38 extending between the poles thereof as shown in Fig. 2 to secure the magnet to the bracket 3 and against a downturned rear flange 40 on the bracket. A portion of bracket 3 is also bent downwardly to extend between the poles of magnet 32, as indicated at 42, with a contact 4:1 riveted to this portion 42 to cooperate with the relatively movable contact 26.

An angle bracket 46 which is secured to the base 2 as by rivet 4B is adapted to receive a limit screw 5!! which is formed with spaced shoulders 52 and 54 with a reduced portion 56 between the shoulders. Ihis reduced portion is adapted to be received within a slot 58 in the upper end of the bimetal member 5 so that the upper end of such member may move only between the limits defined by the shoulders on screw 59. It will be apparent that thescrew may be rotated and adjusted relative to the bracket 46 to obtain the desired initial position of the bimetal members iand 6, as will be described hereinafter.

A lever 60 is pivotally mounted on a pin 62 secured to the base 2 with a helical spring 64 around pin 62 having one end engaging the lever and the other end engaging a stop pin 66 to urge the lever 60' in a clockwise direction. The free end of lever 66 is provided with a contact 66 which is adapted to cooperate with a relatively fixed contact 10 mounted on the bracket 52 on base 2. Secured to the lever 60 is a depending arm It which is provided with a forked lower end it; to straddle an extended end of the armature 38.

Referring now to the operation of the construction described above it will first be noted that the movement of the bimetal member 4 under the influence of the electric heating element [2 is adapted to operate two pairs of contacts, namely, contacts 26 and 44 and contacts 68 and ll). In the normal position both pairs of contacts are closed with the armature 30 in its attracted position and close to but not touching the poles of the magnet 32 as shown in Figure 2. In this position the contact spring 24 is under tension and does not engage against the bimetal member 4 adjacent its upper end to thereby permit a slight amount of give between contact 2'5 and contact 44 and provide a slight wiping engagement between such contacts during closing thereof.

It will also be noted that in the normal pcsition illustrated in the drawing, the armature 36 by its engagement within the forked end 16 of arm 14 holds the contact 68 in engagement with contact 10 against the tension of spring 64 which tends to open such contacts.

When current is supplied to the electric heating element or resistance wire l2 and this wire is heated, the bimetal member 4 will warp to the left or away from the magnet 32. Since a certain amount of energy must be stored up in the bimetal member 4 to overcome the attraction of the magnet, the armature 30 will be suddenly re leased after a predetermined period to separate contacts 25 and 44 with a snap action, and at the same time permit contact 68 to be quickly moved away from contact 10 -by the spring 64 and positively separate such latter contacts if the spring 64 fails to do so.

As shown in Figure 2, the upper end of the bimetal member 6 is in engagement with the shoulder 54 on limit screw 50 and the relation of members 4 and 6 is such-that member 5 actually engages shoulder 54 with suflicient tension to maintain such engagement during all normal operation of the switch mechanism. This tension is opposed to the force of magnet 32 and shoulder 54 constitutes an abutment for the movement of the upper end of member 4 when the latter is heated by the electric heating element l2.

It will be apparent that the adjustment of screw 59 therefore permits a change in the tension exerted by member 6 which will vary the force thereof which is opposed to the action of magnet 32 and thus change the timing of the thermal switch, or in other words, change the length of time that it will take for the upper end of member 4 to warp sufficiently under the influence of the electric heating element 12 to overcome the attractive force of the magnet and open the contacts 25 and 44. As noted above, the member 8 is ordinarily maintained at all times in engagement with shoulder 54, and shoulder E2 is provided merely to prevent excessive tilting in cases of jar or some mechanical dislodgment.

It has also been heretofore noted that members 4 and 6 are constituted of such materials that they will tend to warp in the same relative direction when subjected to the same temperature changes. Thus, member 5 functions through the pivoted bracket 8 to compensate for ambient temperature changes and maintain the upper end of member 4 with the movable contact 26 and armature 39 in substantially the same position with reference to the fixed contact 44 and magnet 32 whenever said members 4 and 6 are both subjected to any change in environment temperature.

Another feature of this invention resides in the relation between the sets of contacts 25-44 and 68-10. For reasons to be mentioned hereinafter in describing one application of the present switch mechanism, it is desired that contacts 26-44 should always close prior to contacts 68-10, and this result is obtainable in the structure shown herein by the mounting of contact 26 on member 4 by the spring 24. The arrangement is such that when the current supply to the electric heating element I2 is discontinued and member 4 cools and the upper end thereof moves toward the magnet 32, the contact 26 will be held by spring 24 which will then lie closely adjacent member 4 so as to first engage the relatively fixed contact 44 and yield during such continued movement of member 4 toward the magnet 32 as is necessary to move lever 60 sufficiently to engage the contact 68 with the relatively fixed contact 10.

As was mentioned heretofore the present switch iechanism was primarily designed for use in a control system for a domestic oil burner. Since the control system is no part of the present invention it is not believed necessary to illustrate the same but the use of the switch mechanism therein will be briefly described.

It is contemplated, for instance, that contacts 26 and 44 would be provided in the ignition circuit to control the operation of suitable ignition means, and contacts 68 and 10 would be provided in a starting circuit to prevent initial operation of the burner unless the ignition circuit is closed by contacts 26 and 44. When current is supplied to the burner motor in response to closure of the room thermostat in known manner, it is contemplated that current will then be supplied through contacts 26 and 44 to the ignition means and the electric heating element l2 will also be energized. The element l2 will become heated and transmit heat to the bimetal member 4 so that after a predetermined time such member will move sufiiciently to open the contacts 26 and 44 in the manner heretofore described to deenergize the ignition circuit, and also open the contacts 68 and 10 in the starting circuit. It is further contemplated that a small amount of current will be supplied to the heating element 12 during operation of the burner which will be sufficient to keep such contacts open but that when the burner shuts off, the current to element l2 will be interrupted and after a predetermined time delay the bimetal member 4 will cool suificiently to close such contacts in the ignition and starting circuits. As has been described above with reference to the switch mechanism, the same is so arranged that the contacts 26 and 44 in the ignition circuit will always close slightly prior to the contacts 68 and 10 in the starting circuit so that the burner motor can never start until the ignition circuit is completed.

It will be obvious however that the present switch mechanism may be used in other applications and that the present invention is not in any way limited to the particular use described above. It will be understood that I also contemplate all such changes and modifications in the specific construction shown herein as may come within the scope of the appended claims.

I claim:

1. In a thermally actuated switch, a bimetal member having one end thereof relatively fixed, an electric heating element mounted adjacent one side of said member, a contact spring secured to the other side of said member and carrying a movable contact adjacent the free end of said member, said member being formed to permit said contact to extend therethrough to the other side thereof, an armature secured to said side of said member, and a relatively fixed contact and magnet adapted to cooperate with said movable contact and armature. a

2. The combination of elements set forth in claim 1 in which said armature is provided with an opening through which said movable contact extends to engage said relatively fixed contact.

3. The combination of elements set forth in claim 1 in which said magnet is of U-shape and said relatively fixed contact is positioned between the poles thereof.

4. In a thermally actuated electric switch, a first bimetal member, a movable contact carried by said member adjacent the upper end thereof, a relatively fixed contact adapted to cooperate with said movable contact, a second bimetal member substantially parallel to said first member, a pivotally mounted bracket connecting the lower ends of said members, and adjustable means to limit the movement of the upper end of said second bimetal member in both directions.

5. The combination of elements set forth in claim 4 with an electric heating element mounted adjacent to said first bimetal member.

6. In a thermally actuated electric switch, a first bimetal member, a movable contact and an armature carried by said member adjacent the upper end thereof, a relatively fixed contact and magnet adapted to cooperate with said movable contact and armature, a second bimetal member substantially parallel to said first member, a pivotally mounted bracket connecting the lower ends of said members, an electric heating element mounted adjacent said first member, and means to limit the movement of the upper end of said second member, said second member being adapted to exert a tension on said first member in opposition to said magnet and compensate for ambient temperature changes.

7. The combination of elements set forth in claim 6 in which said limit means is adjustable to vary the tension exerted by said first member and thereby adjust the timing of the switch operation by said electric heating element. a

8. In a thermally actuated switch, a bimetal member having one end thereof relatively fixed, an electric heating element adjacent said member, an armature secured to said member adja cent the free end thereof, a relatively stationary magnet adapted to cooperate with said armature, a pivoted lever having a forked end to receive the free end of said member, a contact carried by said lever and a relatively fixed contact adapted to cooperate therewith.

9. In a thermally actuated switch, a bimetal member having one end thereof relatively fixed, an electric heating element adjacent said member, a movable contact carried by said member adjacent the free end thereof, a relatively fixed contact adapted to cooperate with said movable contact, a lever engaging the free end of said member, a contact carried by said lever and a relatively fixed contact adapted to cooperate therewith, whereby both sets of contacts will open and close in response to movement of said bimetal member, said movable contact being spring mounted on said bimetal member and so arranged as to engage its cooperating stationary contact on a predetermined movement of said bimetal member prior to engagement of said lever carried contact with its cooperating stationary contact of further movement of said bimetal member.

VAUGHN H. HARDY. 

